1. Field of the Invention
The present invention relates to an image forming apparatus such as, a copying machine or a printer, having a function of forming images on a recording material such as a sheet.
2. Description of the Related Art
An image forming apparatus that transfers a toner image to a recording material by conveying the recording material so that the toner image borne on an image bearing member (a photosensitive drum or an intermediate transfer member) is superimposed on the recording material at a transfer portion is widely used. In such an image forming apparatus, in the process in which the recording material passes through the transfer portion, a discharge electrode as a neutralization member is sometimes disposed on the downstream side of the transfer portion in order to neutralize surplus charges injected to the recording material and to enhance separation of the recording material from the image bearing member. Japanese Patent Application Publication No. 2010-96921 discloses a configuration in which a neutralization needle as a discharge electrode is disposed on the downstream side of a transfer portion which uses a transfer roller as a transfer member.
However, the current-voltage characteristics (hereinafter referred to as I-V characteristics) between the transfer roller and the neutralization needle change depending on an individual difference (a positional relation between the transfer roller and the neutralization needle, a transfer roller resistance, and a neutralization needle shape) of the transfer unit, contamination of the neutralization needle with a long period of use, and the like.
Thus, if the voltage applied to the neutralization member is fixed, a sufficient neutralization effect may not be obtained or a surplus neutralization effect may be obtained depending on a change in the I-V characteristics.